infectious diseases

“very-sick”-pet-cat-gave-oregon-resident-case-of-bubonic-plague

“Very sick” pet cat gave Oregon resident case of bubonic plague

Surprise plague —

The person’s cat was reportedly extremely ill and had a draining abscess.

A cat, but not the one with plague.

Enlarge / A cat, but not the one with plague.

An Oregon resident contracted bubonic plague from their “very sick” pet cat, marking the first time since 2015 that someone in the state has been stricken with the Black Death bacterium, according to local health officials.

Plague bacteria, Yersinia pestis, circulates cryptically in the US in various types of rodents and their fleas. It causes an average of seven human cases a year, with a range of 1 to 17, according to the Centers for Disease Control and Prevention. The cases tend to cluster in two regions, the CDC notes: a hotspot that spans northern New Mexico, northern Arizona, and southern Colorado, and another region spanning California, far western Nevada, and southern Oregon.

The new case in Oregon occurred in the central county of Deschutes. It was fortunately caught early before the infection developed into a more severe, systemic bloodstream infection (septicemic plague). However, according to a local official who spoke with NBC News, some doctors felt the person had developed a cough while being treated at the hospital. This could indicate progression toward pneumonic plague, a more life-threatening and more readily contagious variety of the plague that spreads via respiratory droplets. Nevertheless, the person’s case reportedly responded well to antibiotic treatment, and the person is recovering.

Health officials worked to prevent the spread of the disease. “All close contacts of the resident and their pet have been contacted and provided medication to prevent illness,” Richard Fawcett, Deschutes County Health Officer, said in a news release.

Fawcett told NBC News that the cat was “very sick” and had a draining abscess, indicating “a fairly substantial” infection. The person could have become infected by plague-infected fleas from the cat or by handling the sick cat or its bodily fluids directly. Symptoms usually develop two to eight days after exposure, when the infection occurs in the lymph nodes. Early symptoms include sudden onset of fever, nausea, weakness, chills, muscle aches, and/or visibly swollen lymph nodes called buboes. If left untreated, the infection progresses to the septicemic or pneumonic forms.

It’s unclear how or why the cat became infected. But cats are particularly susceptible to plague and are considered a common source of infection in the US. The animals, when left to roam outdoors, can pick up infections from fleas as well as killing and eating infected rodents. Though dogs can also pick up the infection from fleas or other animals, they are less likely to develop clinical illness, according to the CDC.

While plague cases are generally rare in the US, Deschutes County Health Services offered general tips to keep from contracting the deadly bacteria, namely: Avoid contact with fleas and rodents, particularly sick, injured, or dead ones; Keep pets on a leash and protected with flea control products; Work to keep rodents out and away from homes and other buildings; and avoid areas with lots of rodents while camping and hiking and wear insect repellant when outdoors to ward off fleas.

According to the CDC, there were 496 plague cases in the US between 1970 and 2020. And between 2000 and 2020, the CDC counted 14 deaths.

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Contact-tracing software could accurately gauge COVID-19 risk

As it turns out, epidemiology works —

Time spent with infected individuals is a key determinant of risk.

A woman wearing a face mask and checking her phone.

It’s summer 2021. You rent a house in the countryside with a bunch of friends for someone’s birthday. The weather’s gorgeous that weekend, so mostly you’re all outside—pool, firepit, hammock, etc.—but you do all sleep in the same house. And then on Tuesday, you get an alert on your phone that you’ve been exposed to SARS-CoV-2, the virus that causes COVID-19. How likely are you to now have it?

To answer that question, a group of statisticians, data scientists, computer scientists, and epidemiologists in the UK analyzed 7 million people who were notified that they were exposed to COVID-19 by the NHS COVID-19 app in England and Wales between April 2021 and February 2022. They wanted to know if—and how—these app notifications correlated to actual disease transmission. Analyses like this can help ensure that an app designed for the next pathogen could retain efficacy while minimizing social and economic burdens. And it can tell us more about the dynamics of SARS-CoV-2 transmission.

Over 20 million quarantine requests

The NHS COVID-19 app was active on 13 to 18 million smartphones per day in 2021. It used Bluetooth signals to estimate the proximity between those smartphones while maintaining privacy and then alerted people who spent 15 minutes or more at a distance of 2 meters or less from a confirmed case. This led to over 20 million such alerts, each of which came with a request to quarantine—quite a burden.

The researchers found that the app did, in fact, accurately translate the duration and proximity of a COVID-19 exposure to a relevant epidemiological risk score. The app assessed a contact’s risk by multiplying the length of contact, the proximity of contact, and the infectiousness of the index case as determined by how long it had been since the index case started showing symptoms or tested positive.

There was an increasing probability of reported infection as the app’s risk score increased: more contacts whom the app deemed were at a high transmission risk did go on to test positive for COVID-19 within the following two weeks than those who were notified but had lower risk levels. (That’s positive tests that were reported by using the app. Some of the high-risk people probably did not test at all, did not report their test results, or did not report them within the allotted time. So this is an underestimation of the correlation between notification of risk and infection.)

More exposure = higher risk

When the researchers separated the factors contributing to the risk of an exposure, they found that duration was the most important indicator. Household exposures accounted for 6 percent of all contacts but 41 percent of transmissions.

One caveat: The app didn’t record any contextual variables that are known to impact transmission risk, like if people live in an urban or rural area, was the meeting indoors or outdoors, was it during the week or over the weekend, was anyone vaccinated, etc. Including such data could make risk assessment more accurate.

Based on their work, the researchers suggest that an “Amber Alert” stage could have been introduced to the app, in which people deemed to have an interim degree of risk would be guided to get a PCR test rather than immediately jumping to quarantine. Including this intermediate Amber Alert population could have significantly reduced the socioeconomic costs of contact tracing while retaining its epidemiological impact or could have increased its effectiveness for a similar cost. Performing analyses like this early on in the next pandemic to determine how it is transmitted might minimize illness and strain on society.

Nature, 2023.  DOI:  10.1038/s41586-023-06952-2

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